A technique for reforming fuel for an internal-combustion engine to improve a fuel consumption rate is proposed in a patent document 1 (i.e., JP-A-2009-144612). The proposed technique includes a reforming-fuel injection valve which injects a reforming-fuel into an EGR passage and a fuel reformer catalyst which reforms the reforming-fuel within the EGR passage. The EGR passage partially returns an exhaust gas of the internal-combustion engine from an exhaust passage to an air-intake passage as an EGR gas. Then, the reforming-fuel injected by the reforming-fuel injection valve and water vapor in the EGR gas is put into a reforming reaction by the fuel reformer catalyst. The reforming reaction produces hydrogen, carbon monoxide, etc. which increases the flammability of the reformed fuel. The reformed fuel is then provided to the air-intake passage of the internal-combustion engine.
However, in such a system that utilizes a fuel reformer catalyst, carbon in the EGR gas may deposit on the reformer catalyst and, over time, accumulation of carbon deposits on the fuel reformer catalyst may deteriorate the fuel reforming capacity of the fuel reformer catalyst.
When the technique in the above-mentioned patent document 1 detects degradation of the fuel reformer catalyst and a deterioration of the fuel reforming capacity, injection of the reforming-fuel by the reforming-fuel injection valve is stopped and an air-fuel ratio of the exhaust gas is controlled to be slightly leaner than a stoichiometric ratio. The leaner air-fuel ratio provides a catalyst recovery control which burns the deposit carbon on the fuel reformer catalyst by supplying oxygen to the catalyst and recovers the fuel reforming capacity of the fuel reformer catalyst.
In such a case, while performing the catalyst recovery control which stops an injection of the reforming-fuel, the reforming component density (e.g., density of hydrogen or carbon monoxide) in the EGR gas, which flows back to the air-intake passage, decreases greatly. However, the catalyst recovery control of the above-mentioned patent document 1 stops the injection of the reforming-fuel during the operating the engine (i.e., while the fuel is burned in the engine) for performing the catalyst recovery control. Therefore, when the catalyst recovery control is performed during an operation of an internal-combustion engine, by stopping the injection of the reforming-fuel, the reforming component density in the EGR gas greatly decreases, and the flammability of the internal-combustion engine decreases. For such a reason, a fuel consumption rate improvement effect of the fuel reformer decreases, and exhaust emission and drivability may worsen.